Thanks to the distorting lens of fame, most singers appear shrunken in the flesh. The dislocation between their cultural presence and the bijou package of flesh and bone that comes out on a stage to sing borders on comedy. You'd never ask Lady Gaga to fetch something down off a high shelf barefoot. And let's not even begin enumerating the well-worn Napoleonic parallels suggested by Prince.

And then there's Julian Casablancas. Dressed entirely in black tonight, Casablancas is one of the relatively few stars whose physical stature comes close to matching the shadow he casts over the cultural landscape. (Jack White is another; so is Peter Doherty, arguably).

Should anyone need reminding, back in 2001, the Strokes released Is This It, the album that ushered in a decade of nasal guitar and trousers tailored for deep vein thrombosis. The New York boho-art-band renaissance was their fault. The Libertines were their fault. Arctic Monkeys were their fault. Kings of Leon were their fault. The whole steaming edifice best summarised as UK landfill indie can be laid squarely at their door.

As their decade ebbs, the reconvened Strokes are busy putting the finishing touches on their fourth album, which is PR-speak for "arguing about who's in charge". A perfectionist songwriter, Casablancas once had complete droit de seigneur over the Strokes, a right he surrendered to the need for democracy among this band of schoolfriends who, rumour has it, might have broken up otherwise. Guitarist Nick Valensi is the only Stroke not to have released a solo album in recent years.

As the tinkering goes on, Casablancas is touring his own, terrific, solo album, Phrazes For The Young, an idiosyncratic rewriting of the Strokes songbook replete with keyboards. Casablancas's progress has been dogged by a few bad write-ups. In August, his Japanese debut was reportedly lacklustre; the first night of his UK tour was, apparently, a bit unprofessional.

Reassuringly strapping, Casablancas bumbles around the stage on the final night of this tour, as happy as I've ever seen him. He drinks small cans of something, then throws them hard at the back of the stage. In between songs, this icon of cool blethers with charming inarticulacy ("Shit! I have a cold. I love you guys, man. This shit is awesome! (To himself) Shut up, shut up. Song!").

But he spends his time on tune duty taut and focused. You wouldn't want to mess with Casablancas when he is singing. Even on the sweet-natured country waltz of "Ludlow Street" or the unabashed eighties synth-pop of "11th Dimension", he is intense, gripping the microphone like the gullet of an enemy.

His current band, the Sick Six, are just as locked-on. Unlike, say, the Arctic Monkeys, who have slowed down a little too much, Casablancas seems in as just as much of an amphetaminic hurry as he was when writing Is This It. Of the two drummers, two keyboard players and two guitarists onstage tonight, most double up on other instruments, changing the ratio of drums to guitars to keyboards radically as the set list unfolds. Two songs in, the frenetic "River of Brake Lights" is a four-guitar pummelling that seems designed to frighten off Strokes fans who haven't actually heard Phrazes. With its challenging time signatures, "River" is the kind of track you suspect Casablancas needed to clear from his pipes before a new Strokes record could come out.

Tight and loud, the Sick Six often drown out Casablancas's manful smear of a voice. A new untitled Julian song comes halfway through the set, relentless and pulverising, but it's anyone's guess what it's about.

You suspect being overshadowed by his own music won't bother Casablancas too much. Since the early days of the Strokes, he has used his blackstrap molasses vocals as a layer of sound, one not necessarily at the top of the pile. On Phrazes, that spot is reserved for keyboard melodies; tonight, it's the prattle of electronic drum pads that ices the cake. "Glass" starts as cold as a Neptunes R&B banger ready to hit the clubs, but resolves into bittersweet anthemics, Casablancas crooning washes of syllables that rarely resolve into words.

He'll try anything once, though. Back for the encore, Casablancas is accompanied by just one keyboard player. You can hear him clearly for the first time on this Strokes song, "I'll Try Anything Once", which turns into a mass singalong. Wandering around the photographer's pit hugging most of the front few rows, he wheels out a Christmas song, a delightfully tossed-off tune most would have saved for a straight single.

The night ends with the glorious gospel waltz of "Four Chords of the Apocalypse", whose words start off as clear as day, but end up as chewed as a dog toy, to no ill effect. The next Strokes record will have some way to go to match the heights reached by their frontman.